The present invention relates generally to a solid state fast-neutron spectrometer/dosimeter and a detector therefor. More particularly it relates to a fast neutron detector formed of a substrate of organic semiconductor material coated with a metallic layer forming a Schottky barrier.
Solid state devices for the detection and measurement of various forms of electromagnetic radiation and charged elementary particles are known. A typical solid state radiation detector element may employ a diode that generates an electrical pulse with an amplitude proportional to the ionization density induced in a semiconductor by incident particles. The electrical pulses generated by the diode are organized into a pulse height distribution, which is then analyzed to yield information about the incident radiation.
It is becoming increasingly important to characterize fast-neutron radiation fields. The medical community is now concerned with the tissue damage induced by exposure to fast neutrons. For instance, the fast neutron contamination associated with the use of high-energy medical accelerators requires careful monitoring so that the biological significance of radiation on the eyes and other organs of the body can be assessed.
Several fast-neutron detecting devices have been developed. In order for the dosage received by a body to be properly assessed it is necessary to determine the energy spectrum of the neutron radiation field. In a spectrometer application, the neutron energy distribution is displayed directly. In a dosimeter application, the distribution is integrated to determine the total energy per unit time contributed by the neutron radiation. Neutron spectrometer/dosimeters have generally been rather bulky in comparison with the detectors available for other forms of radiation.
Daniels et al, U.S. Pat. No. 4,217,497 presents an example of one of the more moderately sized devices. Daniels utilizes an organic scintillation detector optically coupled to a photomultiplier. Incident neutrons collide with hydrogen nuclei in the organic scintillator to produce recoil protons, which induce scintillations in the scintillator. The scintillations are optically applied to the photomultiplier which converts them to electrical pulses and amplifies the electronic pulses. A pulse shape discriminator, a multichannel analyzer, and a microcomputer are used to convert the pulse data for spectrometer applications. However, the incorporation of optical couplings and tube-type electronics limits the compactness of the device.
It is also known, as in Kobayashi et al. U.S. Pat. No. 4,210,805, how to detect ionizing radiation with a semiconductor crystal and a barrier layer formed with a metal layer. Slow neutrons have been detected with semiconductor devices having a coating, as of boron, to generate ionizing radiation from incident slow neutrons; see, e.g., Ross U.S. Pat. No. 3,227,876. It is also known how to detect slow neutrons with an organic semiconductor coated with lithium, which captures the slow neutrons and thereupon produces ionizing radiation that is detected as it traverses the semiconductor.
The primary problem in detecting fast neutrons is their great penetrating power. Having no electrical charge, they interact only slightly with atomic electrons in matter, giving up negligible energy to ionization. Because they do not ionize readily, fast neutrons have not been susceptible to detection using the conventional semiconductor technology utilized in measuring charged particle and electromagnetic radiation. A second problem is the differentiation of the fast neutrons from thermal neutrons and other forms of radiation so that the fast neutron field can be accurately assessed.